1. Field of the Invention
The present invention relates to an air bag for a vehicle. More particularly, the present invention relates to an air bag for absorbing a lateral impact applied on a passenger (or passengers) in a vehicle.
2. Description of the Related Art
In the related art, Japanese Patent Application Laid-open No. 2004-268880 discloses an air bag constructed so as to soften a side impact applied on a passenger (passengers) when a vehicle is subjected to a lateral impact. In accommodation, the above air bag is rolled up (folded like a roll) and accommodated in each of side-roof rails. The side-roof rails are positioned on both sides of an upper part of a vehicle body. The air bag is connected to an inflator. When a vehicle has a lateral impact (side collision), the air bag is instantly supplied with gas from the inflator for expansion. Then, the air bag unfolds its expanded body downwardly and enters between a vehicle's side component (e.g. side glass, door, etc.) and a passenger, like a curtain. Owing to this interposition of such a swollen curtain, the air bag serves to absorb an external force from vehicle's sideways to some degree and soften a side impact applied on the passenger in the vehicle, in particular, a passenger's head.
The air bag includes an airbag body like an airtight pouch. The airbag body consists of two sheets of foundation cloths: one in its unfolded state is positioned on the side of a side glass, while the other cloth in the unfolded state is positioned on the side of a passenger. For distinction, the former foundation cloth will be referred to as “outside foundation cloth” hereinafter, while the latter cloth will be referred to as “inside foundation cloth” hereinafter. In production, the periphery (rim) of the outside foundation cloth is joined to the periphery of the inside foundation cloth. In the resulting airbag body, its interior space is divided into a plurality of tubular expansion chambers through a plurality of junctions running up and down in the interior space. Each junction is provided by joining a part of the outside foundation cloth to a part of the inside foundation cloth. In this way, on each side of both foundation cloths, a plurality of tubular expansion chambers are lined up along a fore-and-aft direction of vehicle.
In other words, the airbag body has the tubular expansion chambers arranged in double file along the fore-and-aft direction of vehicle. Here, it should be noted that these tubular expansion chambers are not juxtaposed in the direction of a width of the air bag (referred to as “width direction of airbag” hereinafter) but the uniserial (single file) tubular expansion chambers on the side of the outside foundation cloth are shifted from the uniserial tubular expansion chambers on the side of the inside foundation cloth by half chamber, which seems to be a kind of “alternate” arrangement. That is, in lateral view, respective boundaries among the tubular expansion chambers on the side of the outside foundation cloth do not overlap those on the side of the inside foundation cloth. Such an alternate arrangement of the expansion chambers comes from a consideration that the air bag is preferably formed so as to enable at least one tubular expansion chamber to certainly receive a passenger's head within an entire length of the air bag in the fore-and-aft direction of vehicle.
In view of alleviating a side impact applied on a passenger's head more effectively, however, it is desirable that the air bag is constructed so that two or more tubular expansion chambers may receive a passenger's head on condition that these tubular expansion chambers are piled on each other in the width direction of air bag. In fact, such an improvement is desired in the conventional air bag mentioned above.